Fault handling of inverter driven PM motor drives

ABSTRACT

An apparatus includes a multi-phase inverter, a fault detector to indicate a detection of a fault, a sensor to provide a speed signal indicative of whether a speed of a PM motor is greater than a transition speed, and a controller. The controller is operable to apply either an open-circuit response or a short-circuit response to the multi-phase inverter. The open-circuit response is applied when the speed of the PM motor is greater  less than the transition speed and a fault is detected. The short-circuit response is applied when the speed of the PM motor is less  greater than the transition speed and the fault is detected. The transition speed is either a fixed predetermined speed or an adjusted predetermined speed.

BACKGROUND

The present invention relates to permanent magnetic motor drives. Inparticular, the invention relates to procedures in such drives forhandling faults when detected.

Three-phase voltage inverters are commonly employed to the control themagnitude and frequency of the motor phase currents in hybrid vehicles(including electric and fuel cell powered). When the ac motor used is ofthe class of interior permanent magnet (IPM) type, the reaction of thesystem to various inverter based faults is of concern since the faultmay cause an uncontrolled breaking torque in the motor.

Drive system faults can be classified as short-circuit type faults andopen-circuit type faults. The behavior of various faults in permanentmagnetic motor drives has been reported in the literature for manyyears. Modeling and system behavior of short-circuit type faults aredescribed in B. A. Welchko, T. M. Jahns, W. L. Soong, and J. M.Nagashima, “IPM synchronous machine drive response to symmetrical andasymmetrical short circuit faults,” IEEE Trans. Energy Conversion, vol.18, no. 2, pp. 291-298. June 2003.

For inverter driven IPM motors, an important class of open-circuit typefaults results when the control gate signals to all of the six inverterswitches are turned off, or disconnected. During this condition, themotor is connected to the dc source (e.g., battery, fuel cell, etc.) viathe antiparallel diodes of the inverter switches. The antiparalleldiodes create a potential path for current to flow which is dependantupon the motor operating condition and dc source voltage. The faultcondition where the six gate signals have been turned off has beentermed an uncontrolled generator mode (UCG mode) of operation since themotor would operate during the condition as a generator convertingrotational power into electric currents. Modeling and system behaviorduring UCG mode operation is characterized in T. M. Jahns and V.Caliskan, “Uncontrolled Generator Operation of Interior PM SynchronousMachines Following High-Speed Inverter Shutdown,” IEEE Trans. IndustryApplications, vol. 35, no. 6, pp. 1347-1357, Nov./Dec. 1999.

SUMMARY OF THE INVENTION

In a method example of the invention, a method for controlling amulti-phase inverter of a PM motor includes detecting a fault, sensingwhether a speed signal indicates that a speed of the PM motor is greaterthan a transition speed, and applying either an open-circuit or a shortcircuit response. The open-circuit response is applied when the speed ofthe PM motor is greater less than the transition speed when the fault isdetected. The short-circuit is applied when the speed of the PM motor isless greater than the transition speed when the fault is detected. Thetransition speed is either a fixed predetermined speed or an adjustedpredetermined speed.

In an apparatus example of the invention, the apparatus includes amulti-phase inverter, a fault detector to indicate a detection of afault, a sensor to provide a speed signal indicative of whether a speedof a PM motor is greater than a transition speed, and a controller. Thecontroller is operable to apply either an open-circuit response orshort-circuit response to the multi-phase inverter. The open-circuitresponse is applied when the speed of the PM motor is greater less thanthe transition speed and a fault is detected. The short-circuit responseis applied when the speed of the PM motor is less greater than thetransition speed and the fault is detected. The transition speed iseither a fixed predetermined speed or an adjusted predetermined speed.

In a machine-readable medium example of the invention, themachine-readable medium includes sets of instructions operable in acontroller to cause the controller to perform operations. The sets ofinstructions cause the controller to apply either an open-circuitresponse or a short-circuit response to a multi-phase inverter. Anopen-circuit response is applied when a speed signal from a sensorindicates that a speed of a PM motor is greater less than a transitionspeed when a fault is detected. A short-circuit response is applied whenthe speed signal indicates that the speed of the PM motor is lessgreater than the transition speed when the fault is detected. Thetransition speed is either a fixed predetermined speed or an adjustedpredetermined speed.

BRIEF DESCRIPTION OF DRAWINGS

The invention will be described in detail in the following descriptionof preferred embodiments with reference to the following figures.

FIG. 1 is a schematic diagram of a circuit exemplifying the invention.

FIG. 2 is a graph depicting the phase current of a PM motor as afunction of RPM for both the short-circuit response and the uncontrolledgenerator response as produced by the circuit of FIG. 1.

FIG. 3 is a graph depicting the torque of a PM motor as a function ofRPM for both the short-circuit response and the uncontrolled generatorresponse as produced by the circuit of FIG. 1.

FIG. 4 is a flow chart of an exemplary method of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Embodiments of the present invention apply passive fault responses toinverters that differ depending on the rotational speed of the PM motor.After a fault, the residual control capacity of the faulted system isutilized to guide the system into a controlled fault response thatglobally minimizes the overall fault response characteristic of thesystem, for example, minimizing the uncontrolled breaking torque in themotor. As a result, the envelope of the faulted system response over theoperating space is minimized, and the motor coasts to a stop at acontrolled rate.

In FIG. 1, a circuit for controlling a multi-phase machine that has astator with plural stator windings is depicted. The circuit includes amulti-phase inverter made from a connection of six commutation switches(Q1, D1), (Q2, D2), (Q3, D3), (Q4, D4), (Q5, D5) and (Q6, D6). Thecommutation switches are organized in pairs with each pair connected toa respective phase. Phase A is connected to both the first switch (Q1,D1) and the fourth switch (Q4, D4). Phase B is connected to both thesecond switch (Q2, D2) and the fifth switch (Q5, D5). Phase C isconnected to both the third switch (Q3, D3) and the sixth switch (Q6,D6). The ends of the first, second and third switches that are notconnected to any phase are connected to the PLUS bus. The ends of thefourth, fifth and sixth switches that are not connected to any phase areconnected to the MINUS bus. The six switches are controlled byrespective control inputs C1, C2, C3, C4, C5 and C6. Phases A, B and Cconnect to a permanent magnet motor PM.

A controller provides electronic signals C1, C2, C3, C4, C5 and C6 tocontrol respective commutation switches (Q1, D1), (Q2, D2), (Q3, D3),(Q4, D4), (Q5, D5) and (Q6, D6). A speed sensor senses the rotationalspeed of permanent magnet motor PM and provides a signal characteristicof the rotational speed to the controller.

Controllers of the type used to control am multi-phase permanent magnetmotor are frequently constructed around a micro-processor or equivalent.Other technologies might be used to mechanize a controller ranging fromdiscrete components to application specific integrated circuits (ASICs)and everything between. Such a controller often has built in faultdetection circuitry. Fault detection circuitry detects faults such as“out of limit” conditions, open and short circuit faults or evensoftware faults. Faults may also be detected with separate circuits andreported to the controller as a fault signal. In any case, the fault isdetected by a fault detector, whether the detector is external orinternal to the controller.

For any fault requiring that the motor be shut down in a controlledmanner, one of two fault responses are applied: an open-circuit faultresponse and a short-circuit fault response. The selection of responseto be used depends on the rotational speed of the motor. For purposes ofexample, a transition rotational speed of about 7,000 rpm will beassumed for examples and embodiments discussed herein.

When the motor rotates at rotational speeds below the transition speed,the controller mechanizes the open-circuit fault response by forcing allcommutation switches (Q1, D1), (Q2, D2), (Q3, D3), (Q4, D4), (Q5, D5)and (Q6, D6) to be off (i.e., open circuit). With such a response, themotor is put into an uncontrolled generator mode (UCG mode); however,the motor generates no current (as depicted in FIG. 2) and produces nobreaking torque (as depicted in FIG. 3) when the motor rotates atrotational speeds below the transition speed. On the other hand, if themotor were rotating at rotational speeds above the transition speed, theUCG mode generates increasingly more current (as depicted in FIG. 2)with increasing speed and produces increasingly more breaking torque (asdepicted in FIG. 3) with increasing speed. Therefore, the controlleravoids mechanizing the open-circuit fault response at motor rotationspeeds above the transition speed. Instead, a short-circuit response ismechanized.

A short-circuit response is mechanized by forcing all commutationswitches on the PLUS bus (Q1, D1), (Q2, D2)), and (Q3, D3) to be on(short circuit) while all commutation switches on the MINUS bus (Q4,D4), (Q5, D5) and (Q6, D6) are forced to be off (open circuit).Alternatively, the short-circuit response may be mechanized by forcingall commutation switches on the PLUS bus (Q1, D1), (Q2, D2) and (Q3, D3)to be off (open circuit) while all commutation switches on the MINUS bus(Q4, D4), (Q5, D5) and (Q6, D6) are forced to be on (short circuit). Ineither case, at motor rotation speeds below the transition speed, theshort-circuit response generates increasing more current from the motor(as depicted in FIG. 2) as speed is increased from zero rpm andinitially produces increasingly more breaking torque at low rpm butdiminishing torque as the rpm approaches the transition speed (asdepicted in FIG. 3).

In an embodiment of a method, the method for controlling a multi-phaseinverter of a PM motor being depicted in FIG. 4, the method includesdetecting a fault and sensing whether a speed signal indicates that aspeed of the PM motor is greater than a transition speed. The methodfurther includes applying an open-circuit response when the speed signalindicates that the speed of the PM motor is greater less than thetransition speed when the fault is detected, and applying ashort-circuit response is applied when the speed signal indicates thatthe speed of the PM motor is less greater than the transition speed whenthe fault is detected. The transition speed is either a fixedpredetermined speed or an adjusted predetermined speed.

In a first variant of the method embodiment, the applying theopen-circuit response includes controlling all switches in themulti-phase inverter drive to be open.

In a second variant of the method embodiment, the applying theshort-circuit response includes controlling selected switches in themulti-phase inverter drive to connect all phases of the multi-phaseinverter to a single bus and controlling all other switches in themulti-phase inverter drive to be open.

In a third variant of the method embodiment, the transition speed is thefixed predetermined speed and is defined based on parameterscharacteristic of the PM motor.

In a fourth variant of the method embodiment, the transition speed isthe adjusted predetermined speed and is defined based on parameterscharacteristic of the PM motor adjusted according to either atemperature of the PM motor, or a voltage of a voltage source, or both.

In an embodiment of an apparatus, the apparatus includes am amulti-phase inverter, a fault detector to indicate a detection of afault, a sensor to provide a speed signal indicative of whether a speedof a PM motor is greater than a transition speed, and a controller. Thecontroller is operable to apply an open-circuit response to themulti-phase inverter when the speed signal indicates that the speed ofthe PM motor is greater less than the transition speed and a fault isdetected. The controller is additionally operable to apply ashort-circuit response to the multi-phase inverter when the speed signalindicates that the speed of the PM motor is less greater than thetransition speed and the fault is detected. The transition speed iseither a fixed predetermined speed or an adjusted predetermined speed.

In a first variant of the apparatus embodiment, the application of theopen-circuit response by the controller controls all switches in themulti-phase inverter to be open.

In a second variant of the apparatus embodiment, the application of theshort-circuit response by the controller controls selected switches inthe multi-phase inverter to connect all phases of the multi-phaseinverter to a single bus and controls all other switches in themulti-phase inverter to be open.

In a third variant of the apparatus embodiment, the transition speed isthe fixed predetermined speed and is defined based on parameterscharacteristic of the PM motor.

In a fourth variant of the apparatus embodiment, the transition speed isthe adjusted predetermined speed and is defined based on parameterscharacteristic of the PM motor adjusted according to at least one of atemperature of the PM motor and a voltage of a voltage source.

In an embodiment of a machine-readable medium, the machine-readablemedium includes sets of instructions operable in a controller to causethe controller to perform operations. The sets of instructions areoperable to cause the controller to apply an open-circuit response to amulti-phase inverter when a speed signal from a sensor indicates that aspeed of a PM motor is greater less than a transition speed when thefault is detected. The sets of instructions are further operable tocause the controller to apply a short-circuit response to themulti-phase inverter when the speed signal indicates that the speed ofthe PM motor is less greater than the transition speed when the fault isdetected. The transition speed is either a fixed predetermined speed oran adjusted predetermined speed.

In a first variant of the machine-readable medium, the operator ofapplying the open-circuit response includes controlling all switches inthe multi-phase inverter drive to be open.

In a second variant of the machine-readable medium, the operation ofapplying the short-circuit response includes controlling selectedswitches in the multi-phase inverter drive to connect all phases of themulti-phase inverter to a single bus and controlling all other switchesin the multi-phase inverter drive to be open.

In a third variant of the machine-readable medium, the transition speedis the fixed predetermined speed and is defined based on parameterscharacteristic of the PM motor.

In a fourth variant of the machine-readable medium, the transition speedis the adjusted predetermined speed and is defined based on parameterscharacteristic of the PM motor adjusted according to at least one of atemperature of the PM motor and a voltage of a voltage source.

Having described preferred embodiments of a novel method, apparatus andmedia for handling faults of inverter driven PM motor drives (which areintended to be illustrative and not limiting), it is noted thatmodifications and variations can be made by persons skilled in the artin light of the above teachings. It is therefore to be understood thatchanges may be made in the particular embodiments of the inventiondisclosed which are within the scope of the invention as defined by theappended claims.

Having thus described the invention with the details and particularityrequired by the patent laws, what is claimed and desired protected byLetters Patent is set forth in the appended claims.

1. A method for controlling a multi-phase inverter of a PM motorcomprising: detecting a fault: ; sensing whether a speed signalindicates that a speed of the PM motor is greater than a transitionspeed; applying an open-circuit response when the speed of the PM motoris greater less than the transition speed when the fault is detected;and applying a short-circuit response when the sped of the PM motor isless greater than the transition speed when the fault is detected,wherein the transition speed is one of a fixed predetermined speed andan adjusted predetermined speed.
 2. A method according to claim 1,wherein the applying the open-circuit response includes controlling allswitches in the multi-phase inverter drive to be open.
 3. A methodaccording to claim 1, wherein the applying the short-circuit responseincludes controlling selected switches in the multi-phase inverter driveto connect all phases of the multi-phase inverter to a single bus andcontrolling all other switches in the multi-phase inverter drive to beopen.
 4. A method according to claim 1, wherein the transition speed isthe fixed predetermined speed and is defined based on parameterscharacteristic of the PM motor.
 5. A method according to claim 1,wherein the transition speed is the adjusted predetermined speed and isdefined based on parameters characteristic of the PM motor adjustedaccording to at least one of a temperature of the PM motor and a voltageof a voltage source.
 6. An apparatus comprising: a multi-phase inverter;a fault detector to indicate a detection of a fault; a sensor to providea speed signal indicative of whether a speed of a PM motor is greaterthan a transition speed; and a controller operable to apply anopen-circuit response to the multi-phase inverter when the speed of thePM motor is greater less than the transition speed and a fault isdetected, and additionally operable to apply a short-circuit response tothe multi-phase inverter when the speed of the PM motor is less greaterthan the transition speed and the fault is detected, wherein thetransition speed is one of a fixed predetermined speed and an adjustedpredetermined speed.
 7. An apparatus according to claim 6, wherein theapplication of the open-circuit response by the controller controls allswitches in the multi-phase inverter to be open.
 8. An apparatusaccording to claim 6, wherein the application of the short-circuitresponse by the controller controls selected switches in the multi-phaseinverter to connect all phases of the multi-phase inverter to a singlebus and controls all other switches in the multi-phase inverter to beopen.
 9. An apparatus according to claim 6, wherein the transition speedis the fixed predetermined speed and is defined based on parameterscharacteristic of the PM motor.
 10. An apparatus according to claim 6,wherein the transition speed is the adjusted predetermined speed and isdefined based on parameters characteristic of the PM motor adjustedaccording to at least one of a temperature of the PM motor and a voltageof a voltage source.
 11. A machine-readable medium comprising sets ofinstructions operable in a controller to cause the controller to performoperations comprising: applying an open-circuit response to amulti-phase inverter when a speed signal from a sensor indicates that aspeed of a PM motor is greater less than a transition speed when a faultis detected; and applying a short-circuit response to the multi-phaseinverter when the speed signal indicates that the speed of the PM motoris less greater than the transition speed when the fault is detected,wherein the transition speed is one of a fixed predetermined speed andan adjusted predetermined speed.
 12. A machine-readable medium accordingto claim 11, wherein the operation of applying the open-circuit responseincludes controlling all switches in the multi-phase inverter drive tobe open.
 13. A machine-readable medium according to claim 11, wherriesthe operation of applying the short-circuit response includescontrolling selected switches in the multi-phase inverter drive toconnect all phases of the multi-phase inverter to a single bus andcontrolling all other switches in the multi-phase inverter drive to beopen.
 14. A machine-readable medium according to claim 11, wherein thetransition speed is the fixed predetermined speed and is defined basedon parameters characteristic of the PM motor.
 15. A machine-readablemedium according to claim 11, wherein the transition speed is theadjusted predetermined speed and is defined based on parameterscharacteristic of the PM motor adjusted according to at least one of atemperature of the PM motor and a voltage of a voltage source.